Stabilized photographic sensitive material



Patented Feb. 25, 1941 UNITED STATES PATENT OFFICE STABILIZED PHOTOGRAPHIC SENSITIVE MATERIAL John David Kendall, Ilford, England, assignor to Ilford Limited, Ilford, England, a British com- No Drawing. Application February 11, 1936, Serial No. 63,451. In Great Britain February several forms such as discolouration, growth of chemical fog or an undesirable change of gradation or sensitiveness.

Hitherto many additions have been made to emulsions for the purpose of stabilizing them or rendering them less sensitive to deterioration without impairing their photographic qualities; such additions, apart from soluble bromides and chlorides, include imidazoles and like'comp'ounds forming silver salts the solubility of which does not exceed that of silver chloride, quinine and quinidine and secondary and tertiary aromatic or aromatic aliphatic amines.

According to the present invention, a method of stabilizing photographic materials employing a light sensitive gelatine silver halide emulsion comprises treating the said material with a compound selected from the group comprising 2- mercapto-4-hydroxy pyrimidines, their alkyl, 'aryl and. aralkyl substitution derivatives, their tautomeric compounds and their alkali metal and ammonium salts.

Examples of compounds which may be employed in accordance with the invention are 2- mercapto-i-hydroxy pyrimidines (thio-uracil), G-methyl 2 mercapto- 4 hydroxy pyrimidines (methyl-thimiracil), 5.6.benz-2-mercapto-4-hydroxy-pyrimidines, their tautomeric compounds such as keto-tetra hydro-thio-pyrimidines and their alkali metal or ammonium salts.

The compounds may be incorporated in the photographic emulsion, or they may be incorporated in the support for the sensitive emulsion layer or in an intermediate layer between the sensitive emulsion layer and the support such as the baryta coating commonly used in photographic papers, or they may be incorporated in a protective layer coated upon the emulsion surface, or the otherwise finished photographic material may be bathe-d in a solution containing the compound.

The materials which are normally used in close contact with light sensitive photographic material such as the wrapping materialsused for photographic plates, films and the like may also It is found that photographic materials treated 1 Claim. (Cl. -7)

in accordance with the invention showimprovements in keeping qualities (that is reduction'in fog produced by incubationand/or storage); the contrast remains more constant, and the rate of change of speed on storage is diminished.

In many cases the chemical fog produced on development of the unexposed emulsion is very much reduced, thus permitting the use of longertimes of development, both at high and low temperatures.

The compounds may conveniently be added to an otherwise finished silver halide emulsion in the proportion of from about 1 to cos. of M000 solution per 500 grams of emulsion, 'representing approximately 10 gms. of silver nitrate in the case of slow emulsions as usually employed for preparing positive copies and from about 10- Example I A photographic paper coated with an ordinary gas light emulsion of soft contrast on develop ment under standard conditions (namely in a metol-hydroquinone' developer, as commonly used for gaslightv emulsions) for one minute at 80 F. gave an initial fog of density 0.1, and the same material after incubation for ten days at F. on development under the same conditions gave a fog of 0.18 density. Paper coated with'the same emulsion containing an addition of 0.02 gm. of fi-methyl 2-mercapto-4-hydroxypyrimidine (methyl thio uracil) per 500 gms. of emulsion equivalent to about 10' gms. of silver nitrate developed under the same conditions gave a fog of 0.08 density and after incubation and development under the same conditions as above gave a fog of 0.08 density.

Example II A photographic paper coated witha contrasty gaslight emulsion (silver ehloride-gelatine) on development under the same conditions as in Example I, gave an initial fog density of 0,26, and the same material afterincubation for ten 'days at 115 F'. and developed under the same conditions gave afog density of 0.6.

Paper coated with the same emulsion containing an addition of 0.02 gm. of 6-methyl-2-mercapto-4-hydroxy pyrimidine (methyl-thio-uracil) per 500 gms. of emulsion equivalent to about 10 gms. silver nitrate and treated under the same conditions as 'above gave a fog-density of 0.1 initially and after incubation.

Example III A photographic paper coated with an ordinary silver chlorobromide gelatin emulsion on forced development in a metol hydroquinone developer as commonly used for warm black papers, for two minutes at 100 F. gave a fog density of 1.0 and when developed for twenty minutes at F. in the same developer gave a fog density of 0.10. The same material incubated for ten days at 115 F. and developed under the same conditions gave fog densities of 1.3 and 0.2 respectively. Paper coated with the same emulsion containing an addition of 0.016 gm. of 6-methyl-2-mercapto- 4-hydroxy pyrimidine (methyl-thio-uracil) per 500 gms. of emulsion equivalent to about 10 rams of silver nitrate, and then developed under the same conditions as above gave fog densities of 0.2 and 0.04 respectively which were not increased by incubation.

Example IV A photographic paper coated with a vigorous emulsion of the gaslight type was exposed under a step-wedge and developed under standard conditions in a metol-hydroq uinone developer, as normally used for gaslight emulsions.

The gradation of the negative image was meas ured in the standard manner and the curve of density against log exposure was prepared. It was found that the mean slope of the curve was 4.11 and the maximum slope (gamma) 6.0. Thesame material exposed and developed under the same conditions after incubation for ten days at 115 F. gave a characteristic curve, the mean slope of which was 3.53 and the maximum slope 4.5. Paper coated with the same emulsion treated with an addition of 0.01 gm. of 6'-methyl-2-mercapto-4-hydroxy pyrimidine (methyl-thio uracil) per 500 gms. of emulsion, equivalent to about 10 gms. of silver nitrate, exposed and developed under the same conditions gave a characteristic curve of 3.62 and 4.6 and this material after incubation gave a characteristic curve, the mean slope of which was 3.55 and the maximum slope 4.7. The speed changes on incubation of the untreated and treated material'were not very great.

Example V A photographic paper coated with a normal silver bromide emulsion such as are employed for preparing positivepaper prints, on development under standard conditions for two minutes at F. gave an initial fog density of 0.03 and required an exposure of 24 seconds compared to the standard 25 secs. The same material after incubation 'for ten days at F. gave a fog density of 0.11 andrequired an exposure of 27 seconds.

Paper coated with the same emulsion containing an addition of 0.005 gms. of Z-mercaptoihydroxy pyrimidine (thio uracil) per 500 gms. of emulsion equivalent to '10 gms. silver nitrate on development under the same conditions gave an initial fog of density 0.02 and required an exposure of 29 seconds, and after incubation for ten days at 115 gave an initial fog of 0.03 density and required an exposure of 26 seconds.

Example VI A photographic paper coated with an ordinary vigorous or contrasty gaslight emulsion, on development for one minute at 80 F. under standard conditions in a metol hydroquinone developer,

0.03 density and required an exposure of 5 seconds.

Paper coated with the same emulsion containing an addition of .01 gm. of 5.6-benz-2-mercapto-4-hydroxy pyrimidine per 500 gms. of emulsion equivalent to 10 gms. of silver nitrate treated under the same conditions gave an initial fog of 0.03 and on incubation for ten days at 115 F. gave an initial fog of 0.01 density, with no change in speed.

Example VII Film coated with an ordinary gelatin silver iodobromide emulsion such as are employed for the preparation of negatives, on development under standard conditions, after being kept under normal storage conditions for two weeks, gave an initial fog of density .05, and samples of the same material kept for fourteen days in incubators at F. and relative humidities of 15% and 54% and developed under similar conditions gave initial fog of densities .20 and .23 respectively. Samples of films coated with the same emulsion treated with an addition of 10 cos. of aqueous solution of 2-mercapto-4-hydroxy pyrimidine per unit of emulsion equivalent to 300 gms. silver nitrate and kept and developed under similar conditions gave on development initial fog densities of .05, .13, .12 respectively and the loss of speed was negligible.

Samples of films coated with the same emulsion treated with an addition of 20 cos. of V1000 aqueous solution of 2-mercapto-4-hydroxy pyrimidine per unit and kept and developed under similar conditions gave initial fog densities of .07, .09 and .08 respectively with a just perceptible loss of speed.

Example VIII Samples of films coated with an ordinary gelatin silver iodobromide emulsion intended for the preparation of negatives after being -kept for fourteen days under normal storage conditions and in incubators at 125 F. and relative humidities of 15% and 54% respectively gave on development under standard conditions initial fog densities of .10, .24 and .31 respectively.v Samples of films coated with the same emulsion with an addition of 20 cos. of solution of Z-mercapto- 4-hyd'roxy pyrimidine per unit of emulsion equivalent to 300 gms. silver nitrate, treated under the same conditions gave initial fog densities of .05, .06 and .09 respectively with very little loss of speed. i

The addition of the stabilizing compounds to both silver chloride and silver chlorobromidc 

